Is there anything different between checking for a fallback GUID rather than a regular GUID? I've cloned private schools and public schools I want to check to see if the cloned school was public or private originally.
I've been reluctant to answer this in the hopes someone else may understand your question better than I do. You made them, I assume in SimPE so open them in SimPE and look, that's the same for both GUID and fallback GUID.
If you mean to check them in game with op-codes then there is a massive difference, you can 'set to next object of type' for GUID but not for fallback GUID and you can't 'Test object of type' for fallback GUID. For fallback GUID you'll have to compare the 'Proxy GUID 1' and 'Proxy GUID 2' against your expected values on every item on the lot or at least every item that's in room 0xFFFF ( -1 or off world).
However for custom schools, just like careers the fallback GUID is irrelevant, the fallback GUID is used to choose an item (Maxis default usually) if the cc is removed. There can only be one school of each type so if the cc is removed then so is the school regardless of fallback GUID. Sims assigned to that cc school are not repaired, their person data 0x006B (School Object GUID 1) and person data 0x006C (School Object GUID 2) are left as the now defunct cc and they will have no school. It is better to use the same value for fallback GUID as GUID for things like schools so removal on deletion is complete, that doesn't fix the sims but just prevents the game trying to have two of the same school in existence on a lot.